A study on cooperation and competition between the magnetic correlation and transport properties in systems with localized and itinerant electrons

在这个项目中，我们利用中子散射等微观技术，系统地研究了高温超导体和铀化合物等强关联电子系统的磁序或涨落与超导电性之间的合作或竞争。高温铜酸盐中的超导电性是通过载流子掺杂到Mott绝缘体中而出现的。近年来，在这些铜酸盐中发现了掺杂载流子的自组织，特别是在2-1-4型铜酸盐中。一个主要的问题是，自组织是否普遍存在于其他类型的铜酸盐中，并诱导出新的量子性质，如高温超导。在对铀化合物的研究中，特别是在UPd_2Al_3上，我们完成了一个配对机制的模型，其中U的三个5f电子对该化合物中的超导电性起着不同的作用；一个构筑了一个磁性骨架，另一个通过骨架的磁激发形成了库珀配对。结果表明，该模型不仅可以解释高温超导体的对称性，而且可以解释该体系的许多物理性质。如在UPd_2Al_3中所见，不同类型的电子对高温超导体中对偶力机制的贡献的可能性将是主要问题之一，并将成功地区分本征电子不均匀性和掺杂载流子的化学随机性引起的电子不均匀性。

In this program, we systematically studied cooperation or competition between magnetic order or fluctuation and superconductivity of strongly correlated electron systems such as high temperature superconductors and uranium compounds by using neutron scattering and other microscopic techniques on single crystals with high quality.The superconductivity in the high temperature cuprates appears by carrier doping into the Mott insulators. In recent years, the self-organization of the doped carriers was found in these cuprates particularly in the 2-1-4 type cuprates. One of the main issues is whether the self-organization commonly occurs in other types of cuprates and induces novel quantum properties such as high temperature superconductivity. Although this issue is still continuing, in this program we could provide several key experimental results for the elucidation of this problem.In the study on the uranium compounds particularly on UPd_2Al_3 , we completed a model for the paring mechanism, where three 5f-electrons of U play a role differently for the superconductivity in this compound ; one constructs a magnetic framework and the other forms the Cooper paring through the magnetic excitations of the framework. It turns out this model can explain not only the symmetry of the superconductivity also many of the physical properties of this system.As seen in UPd_2Al_3 the possibility of contribution from different types of electrons for mechanism of the paring force in the high temperature superconductor will be one of the main issues and elucidated if one succeeds in distinguishing the intrinsic electronic inhomogeneity from that caused by the chemical randomness by doping carriers.